Copolyadipamide containing ethyltetramethyleneadipamide units

ABSTRACT

A copolyadipamide consisting essentially of between about 60 and about 99.5 mole percent hexamethyleneadipamide units and between about 0.5 and 40 mole percent ethyltetramethyleneadipamide units, the copolyamide having an RV greater than about 5, and a melting point of greater than about 220° C.

BACKGROUND OF THE INVENTION

The present invention relates to polymers and more particularly to a copolyadipamide having hexamethyleneadipamide units and a minor portion of ethyltetramethyleneadipamide units and products prepared therefrom.

Polyadipamide polymers, e.g., polyhexamethyleneadipamide (nylon 66), have a number of positive characteristics, but are quite thermally unstable at their normal processing temperatures. When kept in the molten state at processing temperature for a long time, polyadipamides form branched/crosslinked, insoluble, nonfusible gel. The formation of gel in the polymer product and on the walls of processing equipment results in deficient product with poor processibility, early when fiber spinning is involved. The fiber spinning breaks which may occur are troublesome and make the winding of large yarn packages impractical.

Certain remedies to gel-formation have been reported such as in U.S. Pat. No. 3,872,055. U.S. Pat. No. 3,872,055 discloses a polyamide composition which has a decreased gel-forming property, specifically a copolyamide of the diamine-dicarboxylic acid type containing a phosphinic or phosphonous acid compound together with an alkali metal compound.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a copolyadipamide consisting essentially of between about 60 and about 99.5 mole percent hexamethyleneadipamide units and between about 0.5 and 40 mole percent ethyltetramethyleneadipamide units, the copolyamide having an RV greater than about 5, and a melting point of greater than about 220° C. For convenience, the copolyamide of the invention will be referred to as nylon 66/Et4-6.

In a preferred form of the invention, the copolyadipamide consists essentially of between about 90 and about 99.5 mole percent hexamethylene adipamide units and between about 0.5 and 10 mole percent ethyltetramethyleneadipamide units. Preferably, the RV of the copolyadipamide is between about 20 and about 80, most preferably between about 20 and about 60.

The copolyamide of the invention provides a reduced gel formation rate relative to that of nylon 66 and provides improvements in product quality, increases in process continuity, and decreases in equipment maintenance costs.

DETAILED DESCRIPTION

The copolyadipamides of the invention are substantially linear copolyamides which consist essentially of between about 60 and about 99.5 mole percent hexamethyleneadipamide units and between about 0.5 and 40 mole percent ethyltetramethyleneadipamide (Et4-6) units. The Et4-6 units can be 1-ethyltetramethyleneadipamide units, 2-ethyltetramethyleneadipamide units or mixtures thereof. In the preferred copolyadipamides, the Et4-6 units are 2-ethyltetramethyleneadipamide units. Preferably, the Et4-6 units are generally randomly distributed throughout the copolymer. The copolyamide has properties similar to homopolymer nylon 66, but has significant advantages in product quality, production cost, and processability.

Depending on the intended end use of the copolyadipamides of the invention, it is advantageous to employ varying mole percentages of Et4-6 in the copolyamide. So that the properties of the copolyamide remain similar to the properties of homopolymer poly(hexamethyleneadipamide), it is preferable for the mole percentage of Et4-6 to be between about 0.5 and about 10%.

The copolyadipamides in accordance with the invention have a formic acid relative viscosity (RV) greater than about 5. Preferably, the RV of the copolyadipamide is between about 20 and about 80, most preferably, between about 20 and about 60.

The melting point of the copolyadipamides in accordance with the invention is greater than about 220° C. The melting points of the copolyadipamides vary with the percentage of Et4-6 and thus range very close to the melting point of homopolymer nylon 66 polymer, about 265° C., when the percentage of Et4-6 is about 0.5%. With increasing Et4-6, the melting point decreases to about 220° C. where the Et4-6 percentage is about 40%.

Surprisingly, the copolyadipamides of the invention have been found to form "gel" at a substantially lower rate than nylon 66 homopolymer. "Gel" refers to the very high molecular weight, branched/crosslinked polymer which forms in the nylon 66 polymer melt and which collects in the product and on equipment walls in contact with the molten polymer. The gel is essentially insoluble and often can only be removed from equipment using extreme measures such as by burning off of the gel. As shown in Table I(c), the gelation time (the time required to show an inflection in a melt viscosity vs. heating time plot of a polymer sample maintained at a constant temperature and constant steam pressure) increases significantly with increasing percentages of Et4-6. In addition, since the melting point of the copolyamide is lower, and is substantially lower at the greater Et4-6 mole percentages, the gelation time can be further increased without affecting spinning performance by employing lower polymer melt temperatures.

The copolyadipamides of the invention can be prepared by condensation polymerization in an aqueous "salt" solution formed by mixing adipic acid with hexamethylenediamine (HMD) and ethyltetramethylenediamine (ETMD) in the molar proportions necessary to produce the copolymer with the desired mole percent of Et4-6 units. In typical procedures, it is desirable to add a slight excess of ETMD to the salt solution. It is believed that the excess may be necessary to produce high quality polymer due to losses of ETMD through cyclization of ETMD to 3-ethylpyrrolidine which occurs during the polymerization. Otherwise, procedures useful for the production of homopolymer poly(hexamethyleneadipamide) have been generally applicable to the production of the copolymer of the invention although polymerization for somewhat longer times at lower temperatures and pressures than normally used for poly(hexamethyleneadipamide) is advantageous in minimizing the loss of ETMD by cyclization.

A particularly convenient method for making a copolyadipamide in accordance with the invention is to provide two aqueous salt solutions of hexamethylene diammonium adipate and ethyltetramethylene diammonium adipate. Necessary quantities of the two solutions can be readily mixed to produce a salt solution for the desired copolyamide.

It is sometimes desirable to add a catalyst to the salt solution. A variety of catalysts are known for use in polymerizing homopolymer nylon 66 such as phenyl phosphinic acid, manganese hypophosphite, etc. The salt solution with or without catalyst is reacted in a suitable reaction vessel such as an autoclave under an inert atmosphere. One preferred procedure is purging the autoclave with nitrogen and increasing the pressure to about 265 psia. The salt solution is heated to a temperature of about 250° C. The pressure is then released over, for example, one hour while increasing the temperature to about 260-275° C. The reaction temperature is held constant at atmospheric pressure for sufficient time to complete the reaction to the extent desired. The copolyamide can be cooled in the autoclave and ground or can be extruded from the autoclave into water and conveniently chipped and dried to produce flake. The RV of the polymer from the clave can be in the range of 5-80 but is typically in the range of 5-45.

The copolyamide in accordance with the invention can also be made by any of a variety of continuous polymerization processes.

The copolyadipamide is useful in a wide variety of known processes for the manufacture of fibers, films, and molded articles. For use of the composition in fibers, any of a variety of known additives such as delustrants, e.g., titanium dioxide, antioxidants, pigments, and other materials may be added to the copolyamide at a suitable point in the polymer preparation or, for example, as the flake is melted in an extruder in advance of spinning.

The following example is offered for the purposes of illustrating the invention and not is intended to be limiting. Percentages are by weight except for the mole percentages of 66 and Et4-6 monomer units and as indicated otherwise. The test methods which follow were used for obtaining the results reported.

TEST METHODS

The formic acid relative viscosity (RV) of the polyamide is measured as described at col. 2, 1. 42-51, in Jennings, U.S. Pat. No. 4,702,875.

Amine and carboxyl ends are determined by the methods described on pages 293 and 294 in Volume 17 of the "Encyclopedia of Industrial Chemical Analysis" published by John Wiley & Sons, Inc. in 1973.

The gel time (reported in hours) is the time required to show a sharp inflection and rise in polymer melt viscosity while heating a polymer sample maintained at a constant temperature and constant steam pressure. A plot of polymer melt viscosity versus time will show a rise or inflection in melt viscosity as formation of polymer gel makes the bulk polymer more viscous. Alternately, gel time can be determined by the method of U.S. Pat. No. 3,872,055. This method reports the time required for making the copolyamide insoluble (when only solvent swelling is observed) in anhydrous formic acid after being heated at a given temperature and pressure in a steam atmosphere.

EXAMPLE I

Into a 300 cc stainless steel autoclave, the following reactants were added in varied amounts as indicated in Table I(a) to provide the indicated mole % ratios nylon 66 salt solution (approximately 50% concentration), adipic acid, and 2-ethyltetramethylenediamine (2-ETMD).

                  TABLE I(a)                                                       ______________________________________                                         Nylon                  Adipic   Nylon                                          66/Et4-6 2-ETMD(g)     Acid(g)  66 Salt(g)                                     ______________________________________                                         100/0    0             0        130                                                                            (51.5%)                                         95/5    2.3           2.1      140                                                                            (51.5%)                                         65/35   14.9          15.5     100                                                                            (51.5%)                                        ______________________________________                                    

For each reactant mixture, the autoclave was purged with nitrogen and sealed. The pressure release valve on the clave was set to 265 psia and the clave was heated to 250° C. When the temperature reached 250° C., the pressure reduction cycle was started so that the pressure was reduced to atmospheric over one hour. At the same time, the temperature of the autoclave was raised to 260° C. When the pressure reached atmospheric, it was held for 60 minutes. The polymer was cooled in the autoclave and removed as a solid block attached to the agitator. The polymer was ground to a fine powder and dried at 90° C. in a vacuum oven over night. Properties of the compositions prepared are reported in Table I(b). The gel times of the 66/Et4-6 copolymers at 292° C. are given in Table I(c).

                  TABLE I(b)                                                       ______________________________________                                                             End Groups                                                                     (Equiv./10.sup.6 g)                                        Nylon 66/Et4-6                                                                           Relative Viscosity                                                                             Amine   Carboxyl                                     ______________________________________                                         100/0     60              41      66                                            95/5     30              39      79                                            65/35    9               36      105                                          ______________________________________                                    

                  TABLE I(c)                                                       ______________________________________                                         Nylon 66/Et4-6                                                                               Gel Time, 292° C., Hr.                                    ______________________________________                                         100/0         15.0                                                              95/5         22.2                                                              65/35        45.0                                                             ______________________________________                                     

We claim:
 1. A copolyadipamide consisting essentially of between about 60 and about 99.5 mole percent hexamethyleneadipamide units and between about 0.5 and 40 mole percent ethyltetramethyleneadipamide units, said copolyamide having an RV greater than about 5, and a melting point of greater than about 220° C.
 2. The copolyadipamide of claim 1 wherein said RV is between about 20 and about
 80. 3. The copolyadipamide of claim 1 wherein said RV is between about 20 and about
 60. 4. The copolyadipamide of claim 1 wherein said ethyltetramethyleneadipamide units are 2-ethyltetramethyleneadipamide units.
 5. A copolyadipamide consisting essentially of between about 90 and about 99.5 mole percent hexamethylene adipamide units and between about 0.5 and 10 mole percent ethyltetramethyleneadipamide units, said copolyamide having an RV greater than about 5, and a melting point of greater than about 220° C.
 6. The copolyadipamide of claim 5 wherein said RV is between about 20 and about
 80. 7. The copolyadipamide of claim 5 wherein said RV is between about 20 and about
 60. 8. The copolyadipamide of claim 5 wherein said ethyltetramethyleneadipamide units are 2-ethyltetramethyleneadipamide units. 